> > Gene has done some testing under CFS with X reniced to +10 and the > > desktop still worked smoothly for him.> > As a data point here, and probably nothing to do with X, but I did > manage to lock it up, solid, reset button time tonight, by wanting > 'smart' to get done with an update session after amanda had started. > I took both smart processes I could see in htop all the way to -19, > but when it was about done about 3 minutes later, everything came to > an instant, frozen, reset button required lockup. I should have > stopped at -17 I guess. :(

yeah, i guess this has little to do with X. I think in your scenario it might have been smarter to either stop, or to renice the workloads that took away CPU power from others to _positive_ nice levels. Negative nice levels can indeed be dangerous.

(Btw., to protect against such mishaps in the future i have changed the SysRq-N [SysRq-Nice] implementation in my tree to not only change real-time tasks to SCHED_OTHER, but to also renice negative nice levels back to 0 - this will show up in -v6. That way you'd only have had to hit SysRq-N to get the system out of the wedge.)